Project Summary (Project 3) Our longstanding focus has been to understand the multiple myeloma (MM) cell- bone marrow stromal cell (BMSC) interactions. We have utilized our in vitro and in vivo models of the MM cell in the bone marrow milieu to identify molecular targets and pathways supporting myeloma cell growth, survival, and drug resistance, and implement effective molecularly-based therapies with dramatic effects on the survival of MM patients. Importantly, rather than focusing on individual targets, our studies integrating various genomic and epigenomic parameters have identified gene regulatory networks as the fundamental mechanisms responsible for continued MM cell growth, despite single targeted therapies. These recurrent and important network motifs form functional nodes in the larger regulatory networks, and are considered to be linchpins of disease causing genomic alterations in MM and other cancers. We hypothesize that aberrant molecular networks drive the progression of MM; confer tumor cell growth and survival advantage; and affect clinical outcome; and that disruption of such circuits will have therapeutic implications. In this project, our robust human MM model systems will be used to stringently validate the role of novel regulatory circuits identified to be of biologic/prognostic significance in Projects 1 and 2 or implicated in disease progression in Project 4; and assess the therapeutic potential of targeting these circuits, both alone and in combination with established and emerging MM therapeutics. We will use our advanced bioinformatic analytical methods to identify gene regulatory networks dysregulated in myeloma and a pooled and/or gene-specific CRISPR screen to evaluate functional impact of each component of the candidate regulatory networks (Specific Aim 1a,b); validate the functional role of selected molecular targets regulating MM cell growth, survival, and drug resistance using our in vitro and in vivo models of human MM in the bone marrow milieu (Specific Aim 1c,d); and evaluate the impact of potential therapeutic agents directed against these validated novel molecular networks, alone and in combination (Specific Aim 2). This proposal will thus improve our understanding of the regulatory circuitry that controls tumor growth and progression in MM, and to develop the next generation of targeted therapies in MM.